Treating printing plates



Patented Nov. 18, 1941 TREATING PRINTING PLATES Daniel Edward McAllister and William Y. Mc-

Intire, Philadelphia, Pa.; said McIntire assignor to said McAllister No Drawing. Application December 10, 1940, Serial No. 369,400

1 Claim.

This invention relates generally to methods of treating photoengravings, electrotypes and other metallic printing plates. It relates more specifically to an improved method for manufacturing a matrix for use in creating in the printing surface of such printing plates depressed highlight and middle tone and other areas.

The art is already familiar with the use of such a matrix in the preparation of printing plates as a means of avoiding the old and well known make ready operation. A method of using such a matrix is described in the United States patent to Henry A. Herr, No. 1,451,162, issued April 10, 1923. The Herr invention is an effort to get away from the old make ready operation with its attendant disadvantages which are well known to the art. There are other operations known to the art for accomplishing the same results as the make ready operation but these also have practical shortcomings which were recognized by Herr in his eifort to provide something better.

The invention herein disclosed is generally directed to the same problem as is the Herr invention and may be approached as an improvement over Herrs efiorts. In the Herr invention the matrix is formed by two etching operations, one on each face of the matrix, which must be in complete registry with each other. There is obviously a substantial danger of inaccuracy in this important registry between the two etched surfaces of the Herr matrix. However, Herr tells the art that proper results cannot be obtained when the matrix is etched on only one surface.

See page 2, lines 84 to 88 of the Herr specification.

The present invention seeks to eliminate this etching on both sides of the matrix, by a method which makes it possible to obtain even better results by etching on only one side of the matrix.

Therefore the main object of this invention is to provide a method of producing printing plates having properly depressed areas on the printing surface thereof in a simpler and more accurate manner than that taught in the prior art. Another object of this invention is the provision of such a method which is susceptible of more positive control in the determination of the amount and extent of depression introduced into the printing surfaces of plates processed according to this method. Another object of this invention is to improve the Herr invention by the avoidance of a step which the art has been taught cannot be avoided; namely, the elimination of the etching of the back surface of the matrix. Still other objects and advantages will become apparent from the following detailed description of a preferred embodiment of this invention. In the following description specific terminology will be employed for the sake of clarity, butit is not intended to thereby limit this invention by the specific terms so selected. On the contrary, it is the intention that each specific term shall include all technical equivalents which operate in a similar manner to accomplish a similar purpose.

In describing the method of this invention, we will start with a printingplate which has already been produced in accordance with well known methods. The printing face of this plate has certain highlight and middle tone areas which must be depressed if the use of a make ready is to be avoided in the functioning of this plate. The plate is first carefully coated on its printing surface with an ink having an oil or varnish base. A proof or impression is then made from the ink coated printing surface of this plate on a hard surface paper. In practice it has been found that an oiled paper and sheets of substances of low absorption qualities such as Cellophane and Celluloid produce good results. The use of other papers and materials may be committed to, the skill of the art. The impression thus obtained on this sheet of paper or other substance is then offset or back printed on a sheet of metal of uniform thickness. It is important that this sheet of metal have a true and smooth surface on both sides thereof; and it may be of copper, brass, zinc, aluminum, bronze or steel. Probably other suitable metals will at once occur to those skilled in the art.

At this stage of the practice of the method it is important to anticipate the necessity of providing means for insuring perfect registry'between the print etched on the printing surface of the printing plate and the print to be etched on the surface of this sheet of metal, which we will now call the matrix. One way of accomplishing this practically is to cut the sheet of paper referred to above to conform exactly to the outside edges of the printing plate. The matrix is also cut to this exact size. In this way it is possible to insure that the subject formed on the surface of the matrix will be in exact registry with the subject formed on the printing surface of the printing plate when the edges are in perfect alignment with each other. Other methods of insuring accurate registration between the subject-matters of the faces of the matrix and printing plate will occur to those skilled in the art.

The matrix having printed on one surfacev subjected to a heat treatment in order to fuse the powder which resisted the brushingoff process. This powder, retained in' the ink coating on certain areas of the printing surface of the plate being processed, forms a very strong acid resisting coat which prevents etching in those areas so covered. It is important that these protected areas have very high acid resisting qualities in order to permit the extended etching action in the unprotected areas which is essential in the practice of this invention. In this way, it is possible to carry the etching of the matrix to sufficient depth that additional etching on the other face thereof becomes unnecessary. In order to preserve the smooth and uniform surface of the reverse side of the matrix, this surface is completely covered with a heavy coating of an "acid resisting agent such as lacquer or wax.

We are now ready to immerse the matrix in an etching bath whose characteristics are determined by the metal selected for the matrix. This is a matter which may be committed to the experience of the art. Satisfactory results have been obtained by the use of ferrous chloride dissolved in water to a density of 40-45 B. for a copper or brass matrix. For a zinc matrix, good results have been obtained from an etching bath made up according to the following proportions: 20 ounces water, 1 /2 ounces sulfuric acid, and /2 ounce nitric acid. It is usually desirable to speed the etching process by moderate agitation of the solution over the immersed matrix in order to quickly gain a sufficient etching depth without exposing the protected areas to too extended contact with the etching bath.

It is possible in the practice of this method to drop back certain middle tone or semi-solid areas without carrying them to the depth of the deeply etched areas by interrupting the etching process at a proper stage and removing the protective coating from such areas on the matrix. The matrix is then again immersed in the etching solution and the result is a printing surface of three diiferent heights comparatively speaking. Additional tones may be likewise obtained by repeating this step at intervals.

After the etching operation has been completed. the matrix is then thoroughly cleaned on both sides preferably using a cleansing solution having an alcohol or benzol base and avoiding the use of cleansing solutions having an acid base. Good results have been obtained from the use of a hot solution of caustic soda and water. The cleansing solution is finally rinsed from the matrix with clear water heated to a temperature of 160 F. or more.

- After being carefully dried, the matrix is ready for application to the back of the printing plate. The etched surface of the matrix is placed against the back surface of the printing plate with the corresponding edges of the matrix and printing plate in very careful alignment which insures perfect registry between the two prints etched on the surfaces of the plate and matrix. The carefully aligned plate and matrix are now placed in a powerful press with the back of the matrix directly on the metal bed of the press. A cushion of soft paper or similar material is placed on the printing surface of the printing plate which is being treated according to this method in order to properly distribute pressure over the printing face of the plate and to preventcrushing. A pressure of about 200 tons has produced satisfactory results in the performance of this step of the method, but this pressure will have to be adjusted to the characteristics of the plate and matrix which is being treated. Obviously different kinds of metals will require variations in the pressures applied thereto in the performance of this step. After the back of the printing platehas been removed from the press and leveled up, the plate is finished and ready for use. The original matrix can, of 'course, be used again for duplicate plates of the same subject, and because it is etched on only one side it will last longer than if it were etched on both sides according to the Herr teaching. The application of heavy pressure to only one etched face is less destructive because of the strengthening effect of the perfectly fiat back face of the etched matrix. This in itself is an advantage over the Herr matrix.

From the above description it will be seen that this invention eliminates from the Herr method an extra step requiring the difficult preservation of registry between surfaces bearing identical prints. This reduces the possibility of error to that extent and also simplifies the treatm'ent'of printing plates to avoid the use of the old make ready. While we have described the preferred embodiment of this invention in considerable detail, it will be clear to those skilled in the art that various modifications may be made therein without departing from the spirit of the invention as hereinafter claimed.

Having thus claim:

The method of producing a matrix for use in the treatment of a printing plate which includes described our invention, we

the following steps: applying a printing ink to the printing surface of the printing plate, making an impression of this inked printing surface on a sheet of hard surface material such as paon the inked surface to provide an acid resisting coating, immersing said metallic sheet in an etching bath and deeply etching the metallic sheet to a predetermined depth, and applying the face of the etched metallic sheet to the back of the printing Plate under heavy pressure with the subject-matter of each in register.

D. EDWARD MCALLISTER.

Y. MCINTIRE. 

